Chikungunya fever is an emerging, epidemic disease, caused by an arbovirus and transmitted by the Aedes mosquitoes, of much significance for WHO's South-East Asia Region. The disease has been reported from countries of South and East Africa, South Asia and South-East Asia. In WHO's South-East Asia Region, outbreaks have been reported from India, Indonesia, Myanmar, Sri Lanka, Thailand and Maldives. Massive outbreaks of Chikungunya fever have occurred in recent years in India and in the island countries of the Indian Ocean. Similarly, Maldives reported outbreaks of Chikungunya fever for the first time in December 2006. Although not a killer disease, high morbidity rates and prolonged polyarthritis leading to considerable disability in a proportion of the affected population can cause substantial socio-economic impact in affected countries (WHO, guidelines for prevention&control of Chikungunya fever, 2009).
The Chikungunya virus (CHIKV) is a member of the genus alphavirus and family Togaviridae (reviewed by Strauss and Strauss, 1994, Microbiol Rev 58, 491-562). The alphaviruses are small enveloped single-stranded positive RNA viruses exhibiting a large cell tropism. The viral surfaces are covered in membrane-anchored spikes composed of triplets of heterodimers of the envelope E1 and E2 glycoproteins. The viral spike proteins facilitate attachment to cell surfaces and viral entry. The E1 envelope glycoprotein is a class II fusion protein that mediates low pH-triggered membrane fusion during virus infection. E2 is a 50 kDa type I transmembrane glycoprotein: the first 260 amino acids constitute the ectodomain, followed by about 100 amino acids that form the stem region, a spanning region of 30 amino acids, and a short cytoplasmic endodomain of 30 amino acids (Plenetv, et al., 2001, Cell 105, 127-136; Mukhopadhyay, et al., 2006, Structure 14, 63-73). pE2 (the 62-kDa precursor to the E3 and E2 proteins) and E1 are assembled as heterodimers in the endoplasmic reticulum (Strauss and Strauss, 1994, Microbiol Rev 58, 491-562). After the cleavage of pE2 in the Golgi apparatus to form E3 and E2, the E1-E2 complexes are transported to the plasma membrane (PM). The interaction of the cytoplasmic E2 endodomain with the preassembled nucleocaspid is one of the initial steps in the process of virus envelopment at the PM. Integrity of virion is maintained by direct interactions between E1 and E2 (Strauss and Strauss, 1994, Microbiol Rev 58, 491-562). During the course of alphavirus life cycle, the E2 glycoprotein is responsible for receptor binding. In general, neutralizing antibodies against alphaviruses recognize epitopes in E2 rather than E1 (Roehrig, J. T. 1986. The use of monoclonal antibodies in studies of the structural proteins of togaviruses and flaviviruses, p. 251-278. In S. Schlesinger and M. J. Schlesinger (ed.), The Togaviridae and Flaviviridae. Plenum Publishing Corp., New York).
Biological diagnosis of CHIK virus infection is essentially based on quantitative real-time RT-PCR-based method during the initial viraemic phase (Edwards et al., 2007, J. Clin. Virol. 39, 271-275; Laurent et al., 2007, Clin. Chem. 53, 1408-1414; Parida et al., 2007, J. Clin. Microbiol. 45, 351-357). Serological methods detect anti-CHIK IgM early times after the first clinical manifestations and specific IgG after two weeks (Pialoux et al., 2007, Lancet Infect. Dis. 7, 319-327). However, ELISA and immunodetection assays are poorly specific and sensitive due the cross reactivity of Chikungunya virus with related members of the Semliki Forest (SF) antigenic complex (Greiser-Wilke et al., 1991, J. Clin. Microbiol. 29, 131-137).
More recently, Brehin and colleagues (Brehin et al., 2008, Virology 371, 185-195) have developed some monoclonal antibodies (mAbs) reactive to CHIKV E2 glycoprotein for diagnosis and research purposes, which were also described in WO 2009/031045. The three anti-CHIKV-E2 mAbs showed cross-reactivity with the O'nyong-nyong viral strains Igbo-Ora and ONN-59. CHIKV, Igbo-Ora and ONN-59 are serologically classified in the SF antigenic complex (Strauss and Strauss, 1994, Microbiol Rev 58, 491-562). These monoclonal antibodies are of murine origin, and although they have demonstrated significant reactivity with CHIKV-associates E2 glycoprotein they failed to neutralize CHIKV infection of primate cells in vitro. Besides, a first commercial Chikungunya virus indirect immunofluorescense test (IIFT) is commercialized by Euroimmun AG, Germany for analyzing the CHIKV specific immune response. This test was evaluated by Litzba et al. (Litzba et al., 2008, Journal of virological methods, 149(1), 175-179).
In the recent years, there has been an explosive re-emergence of Chikungunya fever. Thus, although some advances have been undertaken to provide a reliable test allowing the detection and monitoring of CHIKV specific antibodies, there is still a need to develop new anti-CHIKV monoclonal antibodies for diagnosis and research purposes on Chikungunya virus infection.
On the other hand, a specific treatment is not available and there is no approved vaccine for the prevention of Chikungunya fever. Currently, vector control is the only way to prevent and control the outbreaks. Vector control is not an easy task and insecticide spraying is not always effective and desirable (WHO, guidelines for prevention&control of Chikungunya fever, 2009).
Symptomatic treatment is recommended after excluding more serious conditions. Symptomatic or supportive treatment basically comprises rest and use of acetaminophen or paracetamol to relieve fever and ibuprofen, naproxen or other non-steroidal anti-inflammatory agent (NSAID) to relieve the arthritic component. Patients with persistent or chronic phase of arthritis who fail to respond to NSAID may show some response to chloroquine phosphate. The latter may act as a weak broad spectrum antiviral agent apart from being an anti-inflammatory agent. Use of corticosteroids in managing Chikungunya related arthropathy has in general been a contentious issue and has to be the last resort in a clinical decision (WHO, guidelines for prevention&control of Chikungunya fever, 2009).
While there has been extensive work in vaccinology for several other alphaviruses (Rayner et al., 2002, Rev Med Virol 12, 279-296; Nalca et al., 2003, Antiviral Res 60, 153-174); Johnston & Davis, 2004, Arch Virol Suppl 18, 207-220), the history of vaccine development for CHIKV is short and none of these efforts have yet resulted in a licensed vaccine. Recently, a Phase II study was performed with a serially passaged live chikungunya virus (Edelman et al., 2000, Am J Trop Med Hyg. 62(6), 681-5) with good immunogenicity and tolerance results. However, this vaccine seems not to have reached market authorization and further efforts are being made to find a Chikungunya vaccine, see for example the in vivo study on the immunogenicity of consensus-based DNA vaccines against CHIKV performed by Muthumani et al. (Muthumani K. et al., 2008, Vaccine 26(40), 5128-34).
With regards to the immunotherapy strategies against Chikungunya virus infection, the use of a concentrate of human immunoglobulins (IgA, IgM and IgG) has been previously described, as well as F(ab)′2 and/or Fab fragments specific to an arbovirus (i.e. Chikungunya virus) for use as a medicament in the treatment of arbovirosis, see WO 2007/118986.
Furthermore, studies with neutralizing mAbs have been reported for several alphaviruses including Sindbis virus (SIN), Venezuelan equine encephalitis virus (VEE), Ross River virus (RR), Semliki Forest virus (SF), Eastern equine encephalitis virus (EEE) and Western equine encephalitis virus (WEE) (see, e.g. Roehrig, J. T. 1986. The use of monoclonal antibodies in studies of the structural proteins of togaviruses and flaviviruses, p. 251-278. In S. Schlesinger and M. J. Schlesinger (ed.), The Togaviridae and Flaviviridae. Plenum Publishing Corp., New York). Recently, human polyvalent immunoglobulins were purified from plasma samples obtained from donors in the convalescent phase of CHIKV infection, and the preventive and curative effects of these immunoglobulins were investigated (Couderc et al., 2009, J Infect Dis. 2009, 200(4), 489-91). However, to our knowledge, at present no neutralizing monoclonal antibodies against Chikungunya virus have been described, let alone fully human neutralizing antibodies.
Since at present there is no vaccine or specific treatment available on the market to combat the Chikungunya fever, several efforts are being undertaken to obtain a safe and active therapy to be administered to patients suffering from Chikungunya fever and also to obtain a protective therapy against the virus infection. Accordingly, there is a need for providing therapies that are useful in the prevention and/or treatment of the Chikungunya fever.